Cell Organelles

Nucleus The nucleus is the most obvious organelle in any eukaryotic cell. It is enclosed in a double membrane and communicates with the ring cytosol via numerous nuclear pores. Within the nucleus is the DNA responsible for providing the cell with its unique characteristics. The DNA is similar in both cell of the body, but depending on the specific cell type, some genes may be turned on or off thats why a colored cell is different from a pass cell, and a muscle cell is different from a fat cell.When a cell is dividing, the nuclear chromatin (DNA and surrounding protein) condenses into chromosomes that be easily seen by microscopy. Nucleolus The prominent structure in the nucleus is the nucleolus. The nucleolus produces ribosomes, which move out of the nucleus and take positions on the rude endoplasmic reticulum where they argon critical in protein synthesis. Cytosol The cytosol is the soup within which all the other cell organelles reside and where most of the cellular metabol ism occurs.Though mostly water, the cytosol is fully of proteins that control cell metabolism including signal transduction pathways, glycolysis, intracellular receptors, and transcription factors. Cytoplasm This is a collective term for the cytosol plus the organelles suspended within the cytosol. Centrosome The centrosome, or MICROTUBULE ORGANIZING CENTER (MTOC), is an area in the cell where microtubules are produced. Plant and animal cell centrosomes play similar roles in cell division, and both include collections of microtubules, but the dress cell centrosome is simpler and does not fork out centrioles.During animal cell division, the centrioles replicate (make new copies) and the centrosome divides. The result is two centrosomes, each with its own couplet of centrioles. The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a spindle which is responsible for separating replicated chromosomes into the two daughter cells. Centriole(animal cells only) Each centriole is a ring of nine groups of amalgamated microtubules. There are three microtubules in each group.Microtubules (and centrioles) are part of the cytoskeleton. In the complete animal cell centrosome, the two centrioles are arranged much(prenominal) that one is perpendicular to the other. Golgi The Golgi apparatus is a membrane-bound structure with a single membrane. It is actually a stack of membrane-bound vesicles that are important in packaging macromolecules for direct elsewhere in the cell. The stack of larger vesicles is surrounded by numerous smaller vesicles containing those packaged macromolecules.The enzymatic or hormonal contents of lysosomes, peroxisomes and secretory vesicles are packaged in membrane-bound vesicles at the periphery of the Golgi apparatus. Lysosome Lysosomes contain hydrolytic enzymes necessary for intracellular digestion. They are common in animal cells, but rare in plant cells. Hydrolytic enzymes of plant cell s are more often found in the vacuole. Peroxisome Peroxisomes are membrane-bound packets of oxidative enzymes. In plant cells, peroxisomes play a variety of roles including converting fatty acids to excoriation and assisting chloroplasts in photorespiration.In animal cells, peroxisomes protect the cell from its own production of toxic hydrogen peroxide. As an example, white blood cells produce hydrogen peroxide to fling off bacteria. The oxidative enzymes in peroxisomes break down the hydrogen peroxide into water and oxygen. Secretory Vesicle Cell secretions e. g. ductless glands, neurotransmitters are packaged in secretory vesicles at the Golgi apparatus. The secretory vesicles are then transported to the cell surface for release. Cell Membrane Every cell is enclosed in a membrane, a double level of phospholipids (lipid bilayer).The exposed heads of the bilayer are hydrophilic (water loving), meaning that they are compatible with water both within the cytosol and outside of the cell. However, the hidden tails of the phosopholipids are hydrophobic (water fearing), so the cell membrane acts as a protective barrier to the uncontrolled flow of water. Mitochondria Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type.Mitochondria are membrane-bound organelles, and like the nucleus have a double membrane. The outer membrane is fairly limpid. But the inner membrane is highly convoluted, forming folds (cristae) as seen in the cross-section, above. The cristae greatly increase the inner membranes surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP the primary energy source for the cell. Vacuole A vacuole is a membrane-bound dismission that plays roles in intracellular digestion and the release of cellular waste products.In animal c ells, vacuoles are generally small. Vacuoles tend to be large in plant cells and play several(prenominal) roles storing nutrients and waste products, helping increase cell size during growth, and even acting much like lysosomes of animal cells. The plant cell vacuole also regulates turgor pressure in the cell. Water collects in cell vacuoles, pressing outward against the cell wall and producing rigidity in the plant. Without sufficient water, turgor pressure drops and the plant wilts.Cell Wall(plant cells only) Plant cells have a rigid, protective cell wall made up of polysaccharides. In higher plant cells, that polysaccharide is usually cellulose. The cell wall provides and carrys the shape of these cells and serves as a protective barrier. Fluid collects in the plant cell vacuole and pushes out against the cell wall. This turgor pressure is responsible for the crispness of fresh vegetables. Chloroplast(plant cells only) Chloroplasts are specialized organelles found in all higher plant cells.These organelles contain the plant cells chlorophyll responsible for the plants green color. Chloroplasts have a double outer membrane. Within the stroma are other membrane structures the thylakoids. Thylakoids appear in stacks called grana (singular = granum). Smooth Endoplasmic Reticulum Throughout the eukaryotic cell, especially those responsible for the production of hormones and other secretory products, is a vast network of membrane-bound vesicles and tubules called the endoplasmic reticulum, or ER for short.The ER is a continuation of the outer nuclear membrane and its varied functions suggest the complexity of the eukaryotic cell. The smooth endoplasmic reticulum is so named because it appears smooth by negatron microscopy. Smooth ER plays different functions depending on the specific cell type including lipid and steroid hormone synthesis, breakdown of lipid-soluble toxins in liver cells, and control of calcium release in muscle cell contraction. Rough Endopla smic Reticulum Rough endoplasmic reticulum appears pebbled by electron microscopy due to the presence of numerous ribosomes on its surface.Proteins synthesized on these ribosomes collect in the endoplasmic reticulum for transport throughout the cell. Ribosomes Ribosomes are packets of RNA and protein that play a polar role in both prokaryotic and eukaryotic cells. They are the site of protein synthesis. Each ribosome comprises two parts, a large subunit and a small subunit. messenger RNA from the cell nucleus is moved systematically along the ribosome where transfer RNA adds individual amino acid molecules to the lengthening protein chain.Cytoskeleton As its name implies, the cytoskeleton helps to maintain cell shape. But the primary importance of the cytoskeleton is in cell motility. The internal movement of cell organelles, as well as cell locomotion and muscle fiber contraction could not take place without the cytoskeleton. The cytoskeleton is an organized network of three prim ary protein filaments microtubules actin filaments (microfilaments) intermediate fibers